From: Geoff 
To: psnlist 
Sent: Tue, 4 Jun 2013 20:13
Subject: Water/Laser geophone instrumentation


Hello PSN,

TWO ideas to play with,
I was just playing around with a drink container of water. The
container was about 1/3 full. I took a laser pointer and reflected
the laser light off the surface of the water. The reflection seemed
to exhibit motion related to the water from which it was reflected.
NOW,
Would it be possible, to use a setup like this, to detect seismic
motions ?
1. Tub of water of some design.
2. reflected laser light off the surface somehow.
3. laser light sensor to detect disturbances
    down to the nano-meter of motion ??
4. at this moment in time, ignore planes of motion.

Hi Geoff,

****I tried something similar using about 12 ft of rainwater gutter
flat on the ground with sealed ends, part filled with water. There
is a huge system like this in the Cascades. You use a calculated
length to 'slop' oscillate from end to end at a given period, but
you make the water depth shallow enough to give critical
damping. I shone a red semiconductor laser off the centre of the
trough at grazing incidence and looked at the fairly strong
reflection about 40 ft away on a white wall. I had intended to make
a long plastic float and attach a surface silvered mirror to the=20
centre,
to stop ripples due to air currents and to reduce evaporation, but
the quality of the laser beam was so poor that the edges of the spot
were all 'bobbly' and unusable. It might work better with a long
He/Ne laser tube.

In addition, how about an adaptive optics sensor like the
astronomers use to detect tornadic or helical winds in the
atmosphere ?

****What method do these use and what references do you have ?

    Regards,

     Chris Chapman
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